1. Field of the Invention
This invention relates to a radial tire for heavy duty vehicles such as truck, bus and the like, and more particularly to a radial tire having a carcass comprising a plurality of carcass ply layers made of textile cords.
2. Prior Art
A radial tire with the end portions of its carcass ply layers turning round a bead core along a bead filler is known to have a weak area from the edge of a rim flange to the 30 percent point of the distance between the edge of the rim flange and the point where the width of the tire is the largest. Tires tend to have "separation" in this weak area. In this area, the carcass ply layers including their end portions, that turn round the bead core along the bead filler, are in contact with the bead filler. Since the rubber compound used for the carcass ply layers is relatively soft (JIS (Japanese Industrial Standard) hardness 65 and below) and the rubber compound used for the bead filler is relatively hard (JIS hardness 70 and above) the interconnection between the carcass ply layers and the bead filler may not be strong enough. Thus, this area has been suffering from frequent separation.
In addition, the diameter of the textile cords used in the carcass ply layers has affected this tendency. More specifically, relatively thick textile cords are considered to be advantageous for the carcass ply layers, since these thick textile cords would help to reduce the number of the ply to lower the manufacturing cost and to ease the uneven tension in the cords at the inner and outer sides. However, the rubber compound of the carcass ply layers in contact with the bead filler may be damaged because of shearing strain caused by the pressure from the ground; thus, it was not unlikely to have separation in this area.